ME1000 RF Circuit Design. Lab 10. Mixer Characterization using Spectrum Analyzer (SA)

Transcription

1 ME1000 RF Circuit Design Lab 10 Mixer Characterization using Spectrum Analyzer (SA) This courseware product contains scholarly and technical information and is protected by copyright laws and international treaties. No part of this product may be reproduced, copied, or distributed in any form or by any means without expressed written consent from Acehub Vista Sdn. Bhd. The use of the courseware product and all other products developed and/or distributed by Acehub Vista Sdn. Bhd. are subject to the applicable License Agreement. For further information, see Courseware Product License Agreement. Objectives: i. To measure some important characteristics of the frequency mixer with a SA. ii. To understand the frequency conversion principles of the frequency mixer. Equipments and Accessories Required: i. Spectrum analyzer ii. Signal generator iii. ME1000 Receiver unit iv. SMA m-m coaxial cables v. USB cable vi. PC/Notebook with RF Trainer Control Panel installed DreamCatcher TM is the Trade Mark of Dream Catcher Consulting Sdn. Bhd. ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-1/15

2 Note: Turn off the transceiver trainer kit when not in use. The trainer will turn off automatically when no mouse or keyboard action is detected for more than 10 minutes. Always ensure that the casing is grounded to earth and the cover is latched up before powering up the device. Lab 10 Mixer Characterization using SA Basic Equipment Setup CW Signal Generator RF Output Spectrum Analyzer RF Input RF 868 MHz SMA cable SMA cable IF 50 MHz In Out RF In IF Out In Out In Out LNA Down mixer IF band-pass filter IF amplifier Frequency synthesizer USB port USB cable PC/ Notebook RF Out SMA jumper cable LO In LO 818 MHz Receiver unit RF Trainer Control Panel Required accessories SMA m-m coaxial cable PC/Notebook with RF Trainer Control Panel installed USB cable Figure 1 General equipment configuration for mixer measurement using SA ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-2/15

3 Determine the local oscillator (LO) input level using a spectrum analyzer In Out RF In IF Out In Out In Out LNA Down mixer IF band-pass filter IF amplifier Frequency synthesizer USB port USB cable PC/ Notebook RF Out Plo LO In Receiver unit SMA cable Psa_LO RF Trainer Control Panel Spectrum Analyzer RF Input Figure 2 Equipment set up for LO input level determination We must determine the input LO power level to the mixer by connecting the LO directly to the SA as shown in Figure Connect the output of the frequency synthesizer module directly to the SA. 2. On PC/Notebook, launch the RF Trainer Control Panel. Select RX Unit from the board selection and click Connect to RF Trainer. In the Frequency Synthesizer Control area, click Frequency Synthesizer Off to power up the synthesizer. Set the frequency to 818MHz. You will see the frequency synthesizer PCB LED light up on the trainer, and the button text change to Frequency Synthesizer On. 3. Set the following settings for SA: Centre Frequency Span RBW Attenuation : 818 MHz : 10 MHz : 100 khz : 30 db (or auto) ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-3/15

4 N9320A/B setting: [ ] : Hardkey; { } : Softkey Preset to default settings: [Preset/System] > {Preset} Center Freq: [FREQUENCY] > [818] > {MHZ} Span: [SPAN] > [10] > {MHZ} Attenuation: [AMPLITUDE] > {Attenuation} > [30] > {db} RBW: [BW/AVG] > {Res BW} > {100} > {KHZ} OBSERVATIONS/DATA RECORDING a) What is the power level displayed on the SA when LO is power on? LO level measured at SA, MHz = dbm [Use marker function search peak if necessary] b) Determine the actual output power level of the LO. Actual LO output power, Plo = Psa_LO + Loutput_path = dbm db = 2.7 dbm where, Loutput_path = Lcable_sa + Lhalf_path (cable/connector/pcb trace losses found previously) ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-4/15

5 Conversion loss measurement Take note of the following notation used in mixer measurement: SG Psig_gen (SG input power) Pin_RF Pin_LO RF LO IF Pout_RF Pout_IF Pout_LO SA Pout_sa_RF Pout_sa_IF Pout_sa_LO Plo (LO output power) Pin_RF Pin_LO Pout_RF Pout_IF Pout_LO : Input RF power into mixer s RF port : Input LO power into mixer s LO port : Output RF power from mixer s IF port : Output IF power from mixer s IF port : Output LO power from mixer s IF port Pout_sa_RF : Output RF power from mixer s IF port measured at SA Pout_sa_IF : Output IF power from mixer s IF port measured at SA Pout_sa_LO : Output LO power from mixer s IF port measured at SA Figure 3. Notation used in mixer measurement 1. Make the connection as shown in Figure 1. Similarly, power on the mixer by clicking Mixer Off. You will see the mixer PCB LED light up on the trainer, and the button text change to Mixer On. 2. On the RF Trainer Control Panel, click Connect to RF Trainer. In the Frequency Synthesizer Control area, click Frequency Synthesizer Off to power up the synthesizer. Set the frequency to 818MHz. You will see the frequency synthesizer PCB LED light up on the trainer, and the button text change to Frequency Synthesizer On. ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-5/15

6 3. Use the following settings for signal generator (SG): CW Frequency : 868 MHz Power : 15 dbm N9310A setting: [ ] : Hardkey; { } : Softkey Frequency: [Frequency] > [868] > {MHZ} Amplitude: [Amplitude] > [+/-] > [15] > {dbm} Turn on output: [RF On/Off] 4. Use the following settings for SA: Start Frequency : 10 MHz Stop Frequency : 900 MHz Input Attenuation : 20 db (or auto) RBW : 100 khz (or auto) N9320A/B setting: [ ] : Hardkey; { } : Softkey Start Freq: [FREQUENCY] > {Start Freq} > [10] > {MHZ} Stop Freq: {Stop Freq} > [900] > {MHZ} Attenuation: [AMPLITUDE] > {Attenuation} > [20] > {db} RBW: [BW/AVG] > {Res BW} > {100} > {KHZ} ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-6/15

7 OBSERVATIONS/DATA RECORDING a) Plot the mixer output spectrum from 10 MHz to 900 MHz in the following graph by identifying all the origin and converted tones (such as LO, RF or RF ± LO) and their respective output power levels. 50 MHz 818 MHz 868 MHz Output RF power measured at MHz, Pout_sa_RF = dbm Output LO power measured at MHz, Pout_sa_LO = dbm Output IF power measured at MHz, Pout_sa_IF = dbm b) Determine the actual input and output RF power. Use Linput_path and Loutput_path from the previous lab. Input RF power from the SG, Psig_gen = 15 dbm Actual RF input power into the mixer, Pin_RF = Psig_gen MHz RF output power measured at the SA, Pout_sa_RF = dbm = 15 dbm ( 1.165) db = dbm Actual RF output power from the mixer, Pout_RF = Pout_sa_RF + MHz c) Determine the actual IF output power. Use Lcable from previous lab. IF output power measured at the SA, Pout_sa_IF = dbm = dbm db = dbm Actual IF output power from the mixer, Pout_IF = Pout_sa_IF + MHz = dbm db = dbm ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-7/15

8 d) Determine the actual LO input and output power. Find the jumper cable loss which connects LO_in to RF_out, Ljumper as in Lab 1. LO input power measured previously, Plo = 2.7 dbm Actual LO input power into the mixer, Pin_LO = Plo MHz LO output power measured at the SA, Pout_sa_LO = dbm = 2.7 dbm db = dbm Actual LO output power, Pout_LO = Pout_sa_LO + MHz e) Calculate the conversion loss of the mixer. = dbm db = dbm Conversion loss = Actual input RF power (dbm) Actual output IF power (dbm) = Pin_RF Pout_IF = dbm ( 16.26) dbm = db f) Calculate the RF-to-IF isolation of the mixer. RF-to-IF isolation = Actual input RF power (dbm) Actual output RF power (dbm) = Pin_RF Pout_RF = dbm ( ) dbm = db g) Calculate the LO-to-IF isolation of the mixer. LO-to-IF isolation = Actual LO input power (dbm) Actual LO output power (dbm) = Pin_LO Pout_LO = dbm ( ) dbm = db ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-8/15

9 Gain compression measurements 1. Use the same setup as shown in Figure Use the following settings for SG: CW Frequency : 868 MHz Power : 15 dbm N9310A setting: [ ] : Hardkey; { } : Softkey Frequency: [Frequency] > [868] > {MHZ} Amplitude: [Amplitude] > [+/-] > [15] > {dbm} Turn on output: [RF On/Off] 3. Use the following setting for SA: Centre Frequency : 50 MHz Span : 10 MHz Input Attenuation : 30 db (or auto) RBW : 100 khz (or auto) Averaging : On N9320A/B setting: [ ] : Hardkey; { } : Softkey Center Freq: [FREQUENCY] > [50] > {MHZ} Span: [SPAN] > [10] > {MHZ} Attenuation: [AMPLITUDE] > {Attenuation} >[30] > {db} RBW: [BW/AVG] > {Res BW} > {100} > {KHZ} Averaging: [BW/AVG] > {Average} ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-9/15

10 4. Determine the actual IF output power levels at different RF input power levels. OBSERVATIONS/DATA RECORDING a) Fill in the table below. Use Linput_path (db) and Loutput_path (db) found in the previous lab. SG input power, Psig_gen (dbm) Actual RF input power, Pin_RF (dbm) IF output power measured at SA, Pout_sa_IF (dbm) Actual IF output power, Pout_IF (dbm) ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-10/15

11 b) Plot Pout_IF as a function of Pin_RF in the graph above. c) At what output power level is the gain decreased by 1 db compared with the gain at a very low input power level? P1dB output = 8.7 dbm P1dB input = Output P1dB output Gain = 5.2 dbm ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-11/15

12 Image frequency rejection Image frequency is an undesired input frequency in a mixer that produces the same IF as the desired input signal. An image must be rejected prior to mixing because once it has entered the IF chain, the image will be indistinguishable from the desired signal and impossible to filter out. Image rejection is accomplished by placing the necessary filter before the mixer. Image = RF 2IF V IF 50 MHz IF 50 MHz Image 768 MHz LO 818 MHz RF 868 MHz f Figure 4 Image frequency illustration 1. Use the same setup as described previously. 2. Change the settings for the SG to explore the effect of image frequency. CW Frequency : 768 MHz Power level : 15 dbm N9310A setting: [ ] : Hardkey; { } : Softkey Frequency: [Frequency] > [768] > {MHZ} Amplitude: [Amplitude] > [+/-] > [15] > {dbm} Turn on output: [RF On/Off] ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-12/15

13 3. Change the settings for SA to explore the effect of image frequency. Start Frequency : 10 MHz Stop Frequency : 900 MHz Input Attenuation : 20 db (or auto) RBW : 100 khz (or auto) N9320A/B setting: [ ] : Hardkey; { } : Softkey Start Freq: [FREQUENCY] > {Start Freq} > [10] > {MHZ} Stop Freq: {Stop Freq} > [900] > {MHZ} Span: [SPAN] > [10] > {MHZ} Attenuation: [AMPLITUDE] > {Attenuation} > [20] > {db} RBW: [BW/AVG] > {Res BW} > {100} > {KHZ} OBSERVATIONS/DATA RECORDING a) Plot the mixer output spectrum from 10 MHz to 900 MHz in the following graph ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-13/15

14 4. Change to the following settings for the SA to determine the image frequency power level: Centre Frequency : 50 MHz Span : 10 MHz Input Attenuation : 30 db (or auto) RBW : 100 khz (or auto) Averaging : On N9320A/B setting: [ ] : Hardkey; { } : Softkey Center Freq: [FREQUENCY] > [50] > {MHZ} Span: [SPAN] > [10] > {MHZ} Attenuation: [AMPLITUDE] > {Attenuation} > [30] > {db} RBW: [BW/AVG] > {Res BW} > {100} > {KHZ} Averaging: [BW/AVG] > {Average} OBSERVATIONS/DATA RECORDING a) What is the effect at the IF frequency if an image frequency entered the mixer? The IF frequency will have TWO frequencies overlapping and they are NOT separable. b) What is the power level of the image frequency displayed on the SA? Image MHz, Pimage = 12.8dBm [Use marker function search peak if necessary] c) How do we reduce the image problem? Connect a band-pass filter to the RF input, with the stop-band corresponds to the image frequency. d) Connect the RF band-pass filter module before the mixer and determine the power level of the image frequency displayed on SA. Image MHz after filtering, Pimage_filter = 35.4 dbm e) Calculate the image rejection provided by this filter. Image rejection = Pimage_filter Pimage = 35.4 dbm ( 12.8) dbm = 22.6 db ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-14/15

15 Image 768 MHz References Presentation slides, A Seminar on RF Measurement Spectrum Analysis Basics, Agilent Technologies, 2001 Thomas H. Lee, Planar Microwave Engineering, Cambridge University Press, David M. Pozar, Microwave Engineering, 3 rd Edition, John Wiley & Sons, ME1000 RFCD Copyright 2008 Acehub Vista Sdn. Bhd. Lab 10-15/15